1. Field of the Invention
The present invention relates to a planar coil component used as a large current planar transformer (e.g., a resonance transformer used in a resonance type power supply) or as a choke coil etc., to a method for winding end connection thereof and to a resonance transformer.
2. Description of the Related Art
Thin planar transformers are required for power supplies used in such devices as flat panel televisions etc. Because of the large amount of current in resonance transformers, litz wire, stranded wire or parallel wire etc. where multiple wires thickly bundled together, are used for windings. Generally the process for connecting winding ends to the terminals involves binding and soldering the winding ends of a litz or stranded wire etc. to the terminals (pin terminals) disposed on a terminal board of a bobbin. However, the process has the following problems.
(1) When binding the winding ends to the terminal sticking out from a bottom surface of the terminal board an excessive height for a bundled part of the terminal is required and it hinders lowering the height of products.
(2) In order to lower the height of products, a structure using L-pin type terminals with the winding ends bundled and soldered to the flat part of the L-pin type terminals is well known. But when binding and soldering litz wires, stranded wires or parallel wires in a contiguous terminal structure, adjacent bundled up portions of the wires are easily short-circuited in case of soldering. It causes a reduction in quality and reliability, and workability of the soldering also deteriorates.
(3) In order to lower the height of products, even when using L-pin type terminals, the bundled up portion where litz wires, stranded wires or parallel wires bind is of a considerable size. Thus lowering the height of the products is problematic. Even when binding the winding end to a horizontal part of the terminal, it is still necessary to make the terminal board thicker (or make a standoff larger) so that the bundled portion does not stick out from an underside of the terminal board.
(4) When a litz wire, a stranded wire or a parallel wire used for large current is bundled to a pin terminal, there have been problems in workability and quality (a bundled part may be unraveled easily until soldering etc.) because wires are wound on a bobbin and wire ends dispersed to each pin.
(5) When a litz wire, a stranded wire or a parallel wire used for large current is bound and soldered to a pin terminal, it is difficult to form an alloy layer of solder and copper of a winding (it is difficult for soldering that the solder soaks into bundles of thin copper wires). Thus, soldering workability and quality have been problematic.
(6) When a litz wire, a stranded wire or a parallel wire is wound around a bobbin and bundled to terminals, the wire the length of which is for bundling is wasted.
As other example than bundling ends of windings, a method which a primary winding end is clamped for connection to a primary winding terminal is disclosed in Patent Document 1.
[Patent Document 1] Japanese Patent Application Laid-open No. 7-161462.
In Patent Document 1, the primary winding terminal is clamped to a bottom of a mounting side of a bobbin (specific configuration of clamping is not shown). The primary winding end is clamped by a forked clamping part of the primary winding terminal, and it is soldered by passing it through a soldering tank. The method in Patent Document 1 has the following problems.
(1) The primary winding terminal is disposed on the bottom of the mounting side of the bobbin. After the bobbin is mounted to a device board, the terminal is sandwiched between the device board and terminals board of the bobbin, thus it is difficult to dissipate heat from the terminals. When a large current flows through the winding, a problem of heat generation between the terminal and the winding end occurs. The structure does not solve the problems.
(2) The terminal board of the bobbin and the terminal structure correspond to a vertical type transformer (a magnetic core stands vertically with respect to a mounting surface), therefore, the structures are unsuitable for a horizontal type low height transformer i.e., a planar transformer (a magnetic core is parallel to a mounting surface).
(3) Secondary terminals are important for a resonance transformer but there is no ingenious design for secondary terminals disclosed in Patent Document 1.